function s4 () {
    return Math.floor((1 + Math.random()) * 0x10000)
      .toString(16)
      .substring(1)
  }
  
  export default function () {
    return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
      s4() + '-' + s4() + s4() + s4()
  }